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Summary Aerobic respiration is a process common to almost all eukaryotic organisms and involves the controlled oxidation of reduced organic substrates, carbohydrates, lipids, amino acids and organic acids, to CO2 and H2O, in mitochondria. This releases a large amount of free energy which is conserved in the acid anhydride linkages of ATP molecules. In addition, the primary pathways of respiration...
Summary The first eukaryotes are thought to have arisen around 2 billion years ago through symbiosis of an archaebacterial host cell and a eubacterial symbiont (mitochondrial ancestor). The mitochondrion we know today is the result, therefore, of 2 billion years of evolution of this symbiosis. Like modern day bacteria, mitochondria cannot be created de novo but instead must arise from the fission...
Summary The targeting of nuclear encoded proteins to mitochondria requires that they are specifically imported from the pool of all proteins synthesised in the cytosol. This is more complicated in plant cells compared to other cells due to the presence of plastids, whose targeting signals resemble those of mitochondrial targeting signals in many aspects. Although it is generally believed that cytosolic...
Summary Mitochondrial biogenesis and function are dependent on the expression of numerous nuclear genes and of a limited set of genes present in the mitochondrial genome. In higher plants, mitochondrial genes code for subunits of the respiratory chain complexes, a few proteins involved in cytochrome c-type maturation and some components of the mitochondrial translation machinery, such as rRNAs, tRNAs...
Summary There is increasing awareness of the intricate communication networks and signal transduction pathways that link plant organelles. It appears that in some situations altered expression of specific nuclear genes is directed by other organelles. This is referred to as retrograde regulation of nuclear gene expression and is presumably dependent upon some form of retrograde communication (signaling)...
Summary The evolution of plant mitochondrial genomes, unlike their mammalian counterparts, has been characterized by a large variation in genome size, extensive structural rearrangements, a low rate of nucleotide substitutions, and insertion of foreign DNA. Gene content is highly variable, particulary in flowering plants where there has been rampant gene loss and gene transfer to the nucleus during...
Summary Mitochondrial mutations are widespread in the plant kingdom. They are easily detected when they result in maternal-defective or male-sterile plants. Neutral mutations that do not result in visible phenotypes also occur and are likely to be reservoirs for mitochondrial genome evolution. Because plant mitochondrial genes usually exhibit a slow rate of nucleotide Substitution, most of the reported...
Summary Proteomics is a systematic approach to characterize the expressed protein complement (the proteome) present in particular tissues, cells or subcellular fractions under defined conditions. This analysis is based on (a) high resolu-tion Separation of proteins (most often carried out by two-dimensional gel electrophoresis) (b) protein identification (most often carried out by mass spectrometry)...
Summary The so-called “alternative” electron transport protems, the rotenone-insensitive NAD(P)H dehydrogenases and the alternative oxidase, distinguish the inner membrane of plant mitochondria from its animal counterpart. These proteins provide plant tissues possessing them with the potential to modulate the efficiency with which energy is conserved by respiratory electron transport. The activities...
Summary The aim of this chapter is to gather updated understanding of electron flow and H+ flux-linked processes in plant mitochondria. New understanding of molecular mechanisms of redox pumps and ATP synthase are described. Special attention is paid to the non-phosphorylating electron flow pathways and to H+ electrochemical gradient consumers. Partitioning of electrons between ubiquinol oxidizing...
Summary The metabolic communication between plant mitochondria and the cytosol requires the flux of metabolites, nucleotides and cofactors across the inner mitochondrial membrane. This is accomplished by a family of mitochondrial carrier pro-teins (better characterized in animal and yeast) that span the inner membrane lipid bilayer and share distinct common sequence features. Early studies, using...
Summary In all living organisms a great variety of reactions involve transfer of single carbon units from one molecule to another. These one-carbon (C1) reactions play essential roles in major cellular processes including the synthesis of nucleic acids, protein biosynthesis in the organelles, amino acid metabolism, pantothenate biosynthesis, and the biogenesis of many methylated products. One-carbon...
Summary In addition to normal respiratory functions plant mitochondria also serve a unique role in photorespiration, the con-version of glycine to serine, C02, and NH3. Thus this respiratory organelle has a major role in photosynthetic carbon and nitrogen metabolism in the leaves of C3 plants. The key enzyme in this reaction is the glycine decarboxylase multienzyme complex that is the predominant...
Summary The genome-environment interaction is crucial to sustainability and productivity. Environmental triggers have the single most important impact on plant gene transcription, metabolism and physiology. Since plants are sedentary organisms they have to display an extreme metabolic and morphological plasticity in order to withstand and survive unfavorable changes in the local environment. Nevertheless,...
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